The lancing action of a hypodermic needle, often referred to as a “blade”, is generally facilitated by three bevels, or facets, ground on an end portion of a tubular blank (“tube”) from which the blade is formed. These typically comprise a primary facet and two secondary facets, resulting in the blade having three distinct facet intersections when viewed axially. The sharpness of the angle between these ground facets, between each facet and the blade's curved surfaces, along with other factors such as the diameter and thickness of the blade, effect the levels of patient comfort experienced in use.
Despite the number of blades being consumed by the world's populace continuously increasing over the last fifty years, the manner in which they are mass-produced has developed little in the same period. Typically a linear jig holding up to 1,000 tubes is used. The tubes are clamped between two flat plates of the jig and arranged adjacent one another such that their longitudinal axes are parallel, with one end of each of the tubes extending out from the jig in a direction orthogonal to the axis of a grinding wheel. The amount each tube extends out is governed by such factors as the tolerance of the grinding operation, the amount of material to be removed, and the tube material and dimensions.
During grinding of the blades, the jig traverses the length of the grinding wheel to progressively expose all of the tubes clamped in the jig to the grinding wheel. The primary facet is first ground adjacent the ends of all of the tubes, typically with twelve traverses of the linear jig across the face of the grinding wheel, advancing the jig closer to the grinding wheel at the completion of each traverse. Next, one of the flat plates of the jig clamping the tubes is moved relative to the other in a direction orthogonal to the longitudinal axis of the tubes to roll the tubes uniformly through a predetermined angle. This time with only two traverses across the grinding wheel, a first secondary facet is ground adjacent the end of each tube. The tubes are then further rolled about their longitudinal axes through a predetermined angle, and a further secondary facet having a shape corresponding to the first secondary facet is ground, again in two traverses.
Manufacturing blades by this process presents several difficulties. The linear jig relies on achieving parallel alignment of adjacent tubes, with the ends of the tubes between the clamping plates extending out from the jig orthogonal to the longitudinal axis of the grinding wheel, and a uniform clamping pressure being applied to all of the tubes. Precise grinding further depends on accurately rolling the tubes while maintaining this orthogonal angle of the tubes to the grinding face of the grinding wheel. Initial misalignment of the tubes results in inconsistencies between blades ground in the same and different batches, and these inconsistencies and errors are magnified when the tubes are rolled between the grinding of the different facets. This initial misalignment is both difficult to detect and to remedy, being expensive in terms of time to correct, wasted tubes and/or reduced or inadequate quality of the ground blades.
When manufacturing needles for use in certain types of safety syringes that require a slit or flat to be machined in the tube for co-operation with related structure in the body of the syringe, the slit or flat requires a precise alignment with the primary facet. Current practice for the machining of these slits or flats is to employ another operation subsequent to the grinding of the facets, wherein the blades are re-orientated for the further machining operation. This makes the machining of the slits or flats quite a time-consuming operation. This operation becomes further complicated by the need to avoid touching the ground ends of the tubes to determine the exact locations of the already ground facets, as this has the adverse effect of blunting the ground facet edges.
The conventional method of manufacturing blades using a linear jig results in the grinding wheel having wear greater at its axial end sections than at its middle section, resulting from the horizontal traverses of the jig wherein the tubes first come into contact with the wheel at the axial ends of the wheel. Hence, there is a tendency for the grinding wheels to develop a taperered sectional profile from the middle to either end of the wheels which in turn means that the grinding wheels need to be regularly dressed back to a cylindrical profile.
Further, because grinding occurs largely at the two regions adjacent the axial ends of the grinding wheel, there is a tendency for the temperature of the grinding wheel to build up at these regions, even with the substantive use of coolants. With continuous grinding, these “hot spots” can result in the grinding wheel wearing down quicker and a glazing of the grinding wheel in these regions causing possibly the burning of the blades around the regions of the ground facets, and necessitating further dressing of the wheel thus reducing the life of the wheel.
Typically, for each batch of tubes sixteen traverses of the longitudinal length of the grinding wheel by the linear jig are required for grinding the primary and secondary facets. After each traverse of the linear jig across the grinding wheel the linear jig must be stopped and restarted in the opposite direction. This substantive number of traverses of the linear jig, in combination with the stop/start nature of these traverses, makes it a relatively inefficient process.
The above description in relation to the background of the manufacture of hypodermic needles is not intended to be limiting on the scope of the invention but is merely for the purposes of enhancing an understanding of the present invention.